The Yamaha FZ750 is a sportsmotorcycle produced by Yamaha Motor Corporation between 1985 and 1991. The FZ750 is notable for several reasons, perhaps the most radical being the 5-valve cylinder head with a radial arrangement. This became something of a Yamaha trademark, and although disputed in recent years, it was argued that for a given lift, the 3 inlet valves flowed more effectively than conventional twin inlet valves. What was indisputable was that their light weight allowed for faster opening speeds, and softer valve springs, all contributing to theoretical increases in engine speed and thus power outputs. Whatever the scientific merits, the bikes were famous for their linear power delivery, and in 1985 it was still considered impressive to achieve 150mph from a 750 road machine. Yamaha also designed the motor to have a forward-inclined cylinder block, to effectively lower the centre of gravity. As a result, the FZ750 ran a relatively long wheelbase, which hampered it when used for road racing. What was clear was that Yamaha had considered the engine design in the overall package, rather than as had happened before, when engines were created, and then somehow bundled into a chassis. The FZ750 show-cased Yamaha's design skills.
Development
released the FZ750 in 1985. The bike was popular, and competed well against others in the "sport" class of motorcycles. The machine was noticeably narrower than many contemporaries. Yamaha achieved this by placing the alternator behind the cylinders, instead of the more normal position: on the end of the crankshaft.
Design
Engine
The FZ750 uses an all-aluminium, liquid-cooled, transverse-mounted, four-cylinder engine. The complex cylinder head is constructed in two halves, with dual chain-driven overhead camshafts operating 20 valves, 3 inlet and 2 exhaust per cylinder. Valve clearances are adjusted with under-lifter shims. The four 34 mm Mikuni constant-velocity downdraft carburettors are mounted in a bank behind and above the cylinders and feed each cylinder through short intake manifolds. Four exhaust downpipes join a box below the engine where the gases are split to exit through two silencers. The crankshaft is geared directly to the clutch. No counter balancer shaft is used. Starting is by electric starter only. Lubrication is wet sump using a trochoid pump.
Transmission
The FZ750 uses a six-speed sequential close ratiogearbox; the gear shafts are only removable by splitting the crankcase halves. The clutch is of the wet, multi-plate type and is hydraulically operated. Final drive is by O-ring chain and sprockets. A safety feature of the FZ750 is that the engine ignition is cut if first gear is selected with the sidestand down; this is commonplace on modern motorcycles.
Chassis
The frame of the FZ750 is manufactured from mild steel box-section and uses a perimeter layout. The fairing and upper rear section use separate cylindrical tubing sub-frames. The rear shock absorber is placed vertically behind the engine and connects to an extrudedaluminium alloyswinging arm via several forged aluminium rocker arms. The front wheel is held between spring and oil damped forks. Later models of the FZ750 used a front wheel. Early FZ750s used twin ventilated disc brakes for the front wheel with a single ventilated disc at the rear. Later versions used unventilated disks, with four piston calipers on the front.
Electrical system
The FZ750 features a standard 12 voltelectrical system. The alternator and starter motor are mounted behind the cylinders. Yamaha's self-cancelling indicator unit is used and a variable-resistance gauging system is used to monitor engine oil contents with associated warning lights. Nippondenso Transistor Controlled Ignition is used in conjunction with two coils.
